The present invention relates essentially to a method and means for pre-heating the intake air of a supercharged Diesel engine in particular of low compression ratio when operating at low loads.
It is well known in the prior state of the art that for increasing the power of a supercharged Diesel engine, it is possible to increase the pressure of the pre-compressed intake air supplied by the supercharging system and therefore the weight of combustion-supporting air fed into the engine cylinders hence to correlatively increase the amount of fuel injected for every working cycle of engine operation. In supercharged Diesel or like internal combustion engines, the supercharging air is delivered and compressed by one or several exhaust gas-driven turbo-blowers or like turbine-driven boosters or air compressors discharging into the intake manifold of the engine and consisting generally of an air compressor or booster mechanically coupled to a turbine usually driven by the exhaust gases issuing from each exhaust manifold of the engine. It is generally advantageous or necessary to cool the intake air which has thus been heated or warmed through compression by means of at least one final air cooler or aftercooler located between the intake manifold and the compressor to thereby again increase the weight of air forced into the cylinders for a same displaced volume and at the like time to keep the temperature during the working cycle of the engine at a suitable level.
For a given volumetric compression ratio of the engine it is however not possible to indefinitely increase the ratio of supercharging, i.e., the ratio of the actual pressure of the precompressed intake air to atmospheric pressure, hence the pressure of the supercharging air, because with highly supercharged engines excessive combustion pressures would result therefrom which would overstress the component elements, members or parts of the engine. To overcome such a drawback one is then led to reduce the volumetric compression ratio of the engine.
On the other hand such a decrease in the volumetric compression ratio of the engine is subjected to limitation since a decrease below a certain limit value of for instance 12 results however in the inconvenience of making difficult the start and operation under low-load conditions in particular at idling speed, i.e., under no load or slow running conditions of the engine because the temperature of the intake air after pre-compression is not high enough to cause self-ignition of the injected fuel.